Flow sensor

ABSTRACT

A flow sensor comprises a flow restriction disposed within a passage such that a fluid passing through the passage must pass through the flow restriction. The flow sensor also has an upstream pressure sensor coupled to the passage at a point upstream of the flow restriction and configured to measure and provide an upstream pressure of the fluid within the passage, a downstream pressure sensor coupled to the passage at a point downstream of the flow restriction and configured to measure and provide a downstream pressure of the fluid within the passage, and a temperature sensor coupled to the passage and configured to measure and provide a temperature of the fluid within the passage. The flow sensor also includes a flow sensor processor coupled to the upstream and downstream pressure sensors and the temperature sensor and configured to accept measurements therefrom and calculate a compensated flow rate based at least in part on the measured pressures and temperature.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is related to co-pending U.S. application Ser. No.13/931,566, filed Jun. 28, 2013, entitled “MODULAR FLOW CASSETTE,” U.S.application Ser. No. 13/931,418, filed Jun. 28, 2013, U.S. Pat. No.9,433,743, entitled “VENTILATOR EXHALATION FLOW VALVE,” and U.S.application Ser. No. 13/931,496, filed Jun. 28, 2013, entitled “FLUIDINLET ADAPTER”.

BACKGROUND

Field

The present disclosure generally relates to measurement of gas flowrates and, in particular, to accurate measurement of the flow rate ofmultiple gases.

Description of the Related Art

Patients with respiratory injury, such as chronic respiratory failure,may be provided with a respirator to assist with their breathing or, insevere cases, take over the breathing function entirely. Respiratorstypically provide a flow of air, or other breathing gases, at anelevated pressure during an inhalation interval, followed by anexhalation interval where the pressurized air is diverted so that theair within the patient's lungs can be naturally expelled.

Conventional respirators may be configured to accept one or morebreathing gases, for example “pure oxygen” or “heliox 80/20” (a mixtureof 80% helium with 20% oxygen) from external sources. The exact gasmixture delivered to the patient, however, may be a mixture of variousbreathing gases since the specific percentage required for a particularpatient may not be commercially available and must be custom mixed inthe respirator.

It is important to provide precisely the specified flow rate of gas tothe patient, particularly for neonatal patients whose lungs are smalland very susceptible to damage from overinflation.

SUMMARY

It is advantageous to provide an accurate flow measurement of a varietyof gases and gas mixtures over a range of temperatures and flow rates.

In certain embodiments, a flow sensor is disclosed that comprises a flowrestriction disposed within a passage such that a fluid passing throughthe passage must pass through the flow restriction, an upstream pressuresensor coupled to the passage at a point upstream of the flowrestriction and configured to measure and provide an upstream pressureof the fluid within the passage, a downstream pressure sensor coupled tothe passage at a point downstream of the flow restriction and configuredto measure and provide a downstream pressure of the fluid within thepassage, a temperature sensor coupled to the passage and configured tomeasure and provide a temperature of the fluid within the passage, and aflow sensor processor coupled to the upstream and downstream pressuresensors and the temperature sensor and configured to accept measurementstherefrom and calculate a compensated flow rate based at least in parton the measured pressures and temperature.

In certain embodiments, a method is disclosed that includes the steps ofidentifying a fluid passing through a flow restriction, measuring apressure drop across the flow restriction, retrieving compensationparameters that comprise information associated with characteristics ofthe identified fluid flowing through the flow restriction, andcalculating with a processor a compensated flow rate.

In certain embodiments, a ventilator is disclosed that includes anoutput flow channel configured to mate with a supply limb, an input flowchannel configured to accept a gas from a source, and a flow sensor thathas a flow restriction disposed within a passage coupled between theinput flow channel and the output flow channel such that the gas passingthrough the passage must pass through the flow restriction, an upstreampressure sensor coupled to the passage at a point upstream of the flowrestriction and configured to measure and provide an upstream pressureof the gas within the passage, a downstream pressure sensor coupled tothe passage at a point downstream of the flow restriction and configuredto measure and provide an downstream pressure of the gas within thepassage. The flow sensor also has a temperature sensor coupled to thepassage and configured to measure and provide a temperature of the gaswithin the passage and a flow sensor processor coupled to the upstreamand downstream pressure sensors and the temperature sensor andconfigured to accept measurements therefrom and calculate a compensatedflow rate based at least in part on the measured pressures andtemperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide furtherunderstanding and are incorporated in and constitute a part of thisspecification, illustrate disclosed embodiments and together with thedescription serve to explain the principles of the disclosedembodiments. In the drawings:

FIG. 1 depicts a patient using an exemplary ventilator according tocertain aspects of the present disclosure.

FIGS. 2A and 2B are front and rear views of an exemplary ventilatoraccording to certain aspects of the present disclosure.

FIG. 3 is a block diagram of an exemplary flow sensor according tocertain aspects of the present disclosure.

FIG. 4A depicts an exemplary flow cassette according to certain aspectsof the present disclosure.

FIG. 4B is a cross-section of the flow cassette of FIG. 4A according tocertain aspects of the present disclosure.

FIG. 4C is an enlarged view of a portion of FIG. 4B showing an exemplaryflow sensor according to certain aspects of the present disclosure.

FIG. 5 is a flow chart of an exemplary flow measurement processaccording to certain aspects of the present disclosure.

DETAILED DESCRIPTION

It is advantageous to provide an accurate flow measurement of a varietyof gases and gas mixtures over a range of temperatures and flow rates.

The disclosed systems and methods of measuring flow rates andcompensating for the composition of the gas or gas mixture as well asthe temperature of the measured gas provides increased accuracy comparedto flow measurements made within conventional ventilators.

In the following detailed description, numerous specific details are setforth to provide a full understanding of the present disclosure. It willbe apparent, however, to one ordinarily skilled in the art thatembodiments of the present disclosure may be practiced without some ofthe specific details. In other instances, well-known structures andtechniques have not been shown in detail so as not to obscure thedisclosure. In the referenced drawings, like numbered elements are thesame or essentially similar. Reference numbers may have letter suffixesappended to indicate separate instances of a common element while beingreferred to generically by the same number without a suffix letter.

While the discussion herein is directed to a ventilator for use in ahospital, the disclosed concepts and methods may be applied toenvironments, such as a home or long-term care facility, and otherfields, such as deep-sea diving, that would benefit from accurate flowmeasurement of a variety of gas mixtures. Those of skill in the art willrecognize that these same features and aspects may also be applied tothe sensing of flow rates of other fluids besides medical gases.

Within this document, the term “gas” shall be interpreted to mean both asingle material in gaseous form, for example oxygen, and a mixture oftwo or more gases, for example air or heliox. A gas may include water orother liquids in the form of vapor or suspended droplets. A gas may alsoinclude solid particulates suspended in the gas.

Within this document, the term “pure,” when used with reference to agas, means that the gas meets commonly accepted medical standards forpurity and content.

Within this document, the term “heliox” means a mixture of pure oxygenand pure helium. The mixture may contain a designated percentage of eachgas, for example “heliox 70/30” containing approximately 70% helium and30% oxygen. Heliox may contain trace amounts of other gases.

Within this document, the term “temperature sensor” means a deviceconfigured to measure temperature and provide a signal that is relatedto the measured temperature. A temperature sensor may includeelectronics to provide a drive current or voltage and/or measure acurrent or voltage. The electronics may further include conditioning andconversion circuitry and/or a processor to convert the measured value toa signal that may be in analog or digital form.

Within this document, the term “pressure sensor” means a deviceconfigured to measure a gas pressure and provide a signal that isrelated to the measured pressure. A pressure sensor may includeelectronics to provide a drive current or voltage and/or measure acurrent or voltage. The electronics may further include conditioning andconversion circuitry and/or a processor to convert the measured value toa signal that may be in analog or digital form. The pressure may beprovided in absolute terms or “gauge” pressure, i.e. relative to ambientatmospheric pressure.

Within this document, the term “Hall effect sensor” means a deviceconfigured to detect the presence of a magnet or other magnetic elementwithout making physical contact (non-contacting). A temperature sensormay include electronics to provide a drive current or voltage and/ormeasure a current or voltage. The electronics may further includeconditioning and conversion circuitry and/or a processor to convert themeasured value to a signal that may be in analog or digital form.

FIG. 1 depicts a patient 10 using an exemplary ventilator 100 accordingto certain aspects of the present disclosure. In this example, theventilator 100 is connected to the patient 10 a supply tube or “limb”104 and a return or exhaust limb 106. There may be a conditioning module108 coupled to the supply limb 104 that may, for example, warm orhumidify the air passing through the supply limb 104. The supply andexhaust limbs 104, 106 are both coupled to a patient interface device102 that, in this example, is a mask that fits over the mouth of thepatient 10. In other embodiments (not shown in FIG. 1), the patientinterface device 102 may include a nasal mask, an intubation device, orany other breathing interface device as known to those of skill in theart.

FIGS. 2A and 2B are front and rear views of the ventilator 100 accordingto certain aspects of the present disclosure. The ventilator 100 has ahousing 110 with an attached user interface 115 that, in certainembodiments, comprises a display and a touchscreen. In FIG. 2A, it canbe seen that the front of the housing 110 includes a supply port 155 fora supply limb, such as supply limb 104 in FIG. 1, and a return port 150for a exhaust limb, such as exhaust limb 106 in FIG. 1. The return port150 may be mounted over an access door 152 that provides access to afilter (not visible in FIG. 2A) that filters and absorbs moisture fromthe exhaled breath of the patient 10. In certain embodiments, there mayalso be a front connection panel 160 for connection to, for example,external instruments, sensors, or sensor modules. FIG. 2B shows a rearview of the ventilator 100 with a gas inlet adapter 120, an air intakeport 140, and a power interface 130 that may include a power plugconnector and a circuit breaker reset switch. There may also be a rearinterface panel 165 for connection to external instruments or a networkinterface cable. A flow cassette 200 is installed within the housing 110behind the gas inlet adapter 120 and in fluid communication between theinlet connector 126 shown in FIG. 2B and the supply port 155 shown inFIG. 2A.

FIG. 3 is a block diagram of an exemplary flow cassette 200 according tocertain aspects of the present disclosure. The flow cassette 200includes an inlet 222 that is configured to sealingly mate with an inputflow channel, for example a coupler 122 of the gas inlet adapter 120.The gas inlet adapter 120 also has an inlet connector (not shown in FIG.3) that is fluidly connected to the coupler 122. Various breathing gasesand gas mixtures are associated with individually unique connectortypes, sizes, and configurations, wherein the association is generallyrecognized in the medical industry. Each gas inlet adapter 120 has oneor more inlet connectors that are adapted to respectively accept aconnector that is unique to a certain type of gas or gas mixture. Thenumber and placement of magnets 124 are uniquely associated with theinlet connector that will be coupled to the inlet of the flow cassette200 when that gas inlet adapter 120 is installed in a ventilator andthereby mated with the flow cassette 200. In certain embodiments, thegas inlet adapter 120 may be configured to accept one or more of astandard composition of ambient air, a pure oxygen, and a heliox gasmixture.

The inlet 222 is fluidly connected to a passage 223 that runs throughthe flow cassette 200 to an outlet 232 that is configured to sealinglymate with an output flow channel of the ventilator 100 that, forexample, leads to the supply limb 104. In this example embodiment, thereare several elements disposed along the passage 223, including a checkvalve 260, a filter 264, a porous disk 410 and a valve 300. In certainembodiments, some of these elements may be omitted or arranged in adifferent order along the passage 223. In this embodiment, the flowcassette 200 also includes a Hall effect sensor 258 configured to detectthe number and placement of the magnets 124 of the gas inlet adapter120. By comparing the detected number and placement of the magnets 124to stored information associating the number and placement of themagnets 124 with gases that will be accepted by the inlet connector thatis coupled to the inlet of the flow cassette 200, the processor 252 canautomatically determine what gas will be provided through the gas inletadapter 120 as installed in the ventilator 100. In other embodiments,the gas inlet adapter 120 may include another type of indicator, forexample a machine-readable element, that is associated with theconfiguration of the gas inlet adapter 120 and the flow cassette 200 mayinclude a sensor that is capable of reading the machine-readable elementand thereby automatically detecting the configuration of the gas inletadapter 120.

The flow cassette 200 includes a flow sensor 400 that has a flowrestriction 410 that, in this example, is a porous disk disposed inpassage 223 such that all gas flowing through the passage 223 must passthrough the porous disk 410. The flow sensor 400 also includes anupstream pressure sensor 420A and downstream pressure sensor 420B withgas passages 424 from the sensors to sensing ports 421A and 421Bdisposed in the passage 223 on upstream and downstream sides,respectively, of the porous disk 410. There is also a temperature sensor270 that has a temperature sensing element 271 disposed in the passage223. In conjunction with the knowledge of which gas is flowing throughthe porous disk 410, derived from the configuration of the gas inletadapter 120 as indicated by the magnet 128 and sensed by the Hall effectsensor 258, and the knowledge of the temperature of the gas, as measuredby the temperature sensor 270, the pressure drop can be used todetermine the true flow rate, sometimes referred to as “the compensatedflow rate,” of the gas that is passing through the porous disk 410.

The pressure drop across the porous disk 410 is related in a monotonicway to the rate of gas passing through the porous disk 410. The porousdisk 410 is characterized as to its flow resistance characteristics witha selection of gases and gas mixtures at a standard temperature. Withoutbeing bound by theory, certain gases, such as helium, have a smallermolecular size and pass more easily through the thickness of the porousdisk 410 compared to a gas, such as nitrogen, with a larger molecule.Thus, a certain pressure drop will indicate a first flow rate for asmall-molecule gas and a second, lower flow rate for a large-moleculegas. Gas mixtures will tend to have flow rates that reflect thepercentage composition of the gases that make up the gas mixture. Incertain embodiments, the pressure drops of certain predetermined medicalgases and gas mixtures are specifically characterized for the porousdisk 410 and stored in a look-up table contained in the memory 254 ofthe electronics module 250. The temperature of a gas also affects thepressure drop for a given flow rate of that gas flowing through theporous disk 410. In certain embodiments, the effect of the gastemperature is also characterized for the porous disk 410 and stored inthe memory 254. In certain embodiments, the characterization of the flowcharacteristics of the porous disk 410, also referred to herein as“compensation parameters,” are combined for gas type and temperature ina single look-up table. Those of skill in the art will recognize thatsuch compensation parameters may be stored in other forms, for exampleequations that include scaling parameters, to enable conversion of a rawpressure drop measurement into an accurate flow rate.

The flow cassette 200 includes an electronics module 250. In certainembodiments, the conversion of the raw pressure measurements by pressuresensors 420A, 420B into a pressure drop measurement is accomplished in aseparate pressure sensing electronics 422 and provided to a flow sensorprocessor 252. In certain embodiments, the pressure sensing electronics422 may provide the processor 252 with individual pressure signals forpressures that are upstream and downstream of the porous disk 410. Incertain embodiments, there may also be a front connection panel 160 forconnection to, for example, external instruments, sensors, or sensormodules. In certain embodiments, the pressure sensors 420A, 420B mayprovide the raw signals directly to the processor 252. In certainembodiments, the pressure sensors 420A, 420B may include conversioncircuitry such that each sensor 420A, 420B provides a pressure signaldirectly to the processor 252.

In certain embodiments, the temperature sensor 270 provides a signalthat includes a temperature to the pressure sensing electronics 422. Incertain embodiments, the temperature sensor 270 provides thistemperature signal directly to the processor 252. In certainembodiments, the temperature sensing element 271 may be connecteddirectly to the pressure sensing electronics 422 or to the processor252. In certain embodiments, the temperature sensor 270 may beconfigured to sense the gas temperature over a range of temperatures ofat least 5-50° C. In certain embodiments, the temperature sensor 270 maybe configured to sense the gas temperature over a range of temperaturesof at least 5-50° C.

The processor 252 is connected to the memory 254 and an interface module256 as well as the sensors 270, 420A, and 420B. The various drive,sensing, and processing functions of these sensors 270, 420A, and 420Bmay be accomplished in various different modules, such as the processor252 and pressure sensing electronics 422, depending on the particulardesign and layout of the flow cassette 250 without departing from thescope of this disclosure. For example, a processor 252 may be configuredto provide a supply an electrical current directly to the temperaturesensing element 271 and to directly measure a voltage drop across thetemperature sensing element 271 without the need for interveningelectronics. All functions disclosed herein may be accomplished in theblock elements of FIG. 3 as described or in alternate blocks and theblocks depicted in FIG. 3 may be combined or divided without departingfrom the scope of this disclosure.

The memory 254 is configured to store operating instructions for theprocessor 252 and data that may include calibration data for the sensors258, 270, 420A, and 420B. The data may also include information, asdiscussed above, such as equations or look-up tables to use the twopressure measurements from pressure sensors 420A and 420B and thetemperature measurement from the temperature sensor 270 to determine aflow rate through the porous disk 410. In certain embodiments, thememory comprises non-volatile memory such as magnetic disk, asolid-state memory, a flash memory, or other non-transient, non-volatilestorage device as known to those of skill in the art.

The processor 252 is also operatively coupled to the valve 300 and iscapable of actuating the valve 300. The interconnection of the processor252 with the other elements as shown in FIG. 3 may be accomplished bydirect connection via any technology known to those of skill in the art,for example twisted-pair wires or fiber-optic cables, or via a networkconnection with microprocessors embedded in the other elements. Theinterface module 256 may include signal transceivers for wired orwireless communication with other devices within the ventilator 100 ormay connector to an external interface, such as the rear interface panel165 shown in FIG. 2B, to communicate with devices external to theventilator 100.

FIG. 4A depicts an exemplary flow cassette 200 according to certainaspects of the present disclosure. The flow cassette 200 has a body 210with an inlet end 220 and an outlet end 230. At the inlet end 220, thereis the inlet 222 that is configured to sealingly mate with a coupler 122(not shown in FIG. 4A) of a gas inlet adapter 120. The inlet end 220 mayalso include locating features 226, for example protruding pins, thatalign the gas inlet adapter 120 to the inlet 222 and a mating face 224that provides a reference surface for the mated gas inlet adapter 120. Asolenoid 240 is attached to the body proximate to the outlet end 230 todrive a pressure control valve (not visible in FIG. 4A) disposed withinthe body 210. The electronics module 250 is attached, in thisembodiment, to the top of the body 210. The details of the electronicsmodule are discussed in greater detail with respect to FIG. 3.

FIG. 4B is a cross-section of the flow cassette of FIG. 4A according tocertain aspects of the present disclosure. The dashed-line box 400indicates the elements that make up the flow sensor 400, which isdiscussed in greater detail with respect to FIGS. 3 and 4C. The passage223 that connects the inlet 222 and outlet 232 is visible in thecross-section of FIG. 4B, with the porous disk 410 disposed within thepassage 223.

FIG. 4C is an enlarged view of a portion of FIG. 4B showing theexemplary flow sensor 400 according to certain aspects of the presentdisclosure. In this example, the pressure sensors 420A, 420B aredisposed within the package of the pressure sensing electronics 422 andconnected to the passage 223 by gas passages 424 leading to sensingports 421A and 421B. The temperature sensing element 271 is exposed tothe interior of the passage 223 and therefore in contact with the gaswithin the passage 223. Seals 426, in this example a pair of o-rings,provide a gas-tight seal between the housing 210 and the tube extensions428 for the gas passages 424 and a feed-through 429 for the temperaturesensing element 271.

FIG. 5 is a flow chart of an exemplary flow measurement process 500according to certain aspects of the present disclosure. The process 500starts in step 510 by determining which gas or gas mixture, for exampleoxygen or heliox 70/30, will be flowing through the flow sensor 400. Instep 515, the gas pressures upstream and downstream of the flowrestriction 410 are measured and a pressure drop across the flowrestriction 410 is calculated in step 520. In step 525, the processor252 calculates an uncompensated flow rate based at least partially onthe pressure drop. The temperature of the gas flowing through the flowsensor 400 is measured in step 530 and in step 535 the processor 252loads information from the memory 254 that may include compensationparameters related to the flow sensor 400. The processor 252 calculatesa compensated flow rate using the retrieved compensation parameters instep 540 and provides this compensated flow rate, for example to aprocessor of the ventilator 100, in step 545. Step 550 is a decisionpoint that checks whether a “stop” command has been received, in whichcase the process 500 branches along the “yes” path to the end andterminates. If a “stop” command has not been received, the process 500branches along the “no” path back to step 515 and measures the pressuresand temperature. The process 500 will loop through the steps 515-550until a “stop” command is received.

In summary, it can be seen that the disclosed embodiments of the flowsensor provide an accurate measurement of a gas flow rate in a compactand modular form. The accuracy of the flow rate may be improved bycompensating for one or more of the gas temperature and the gascomposition. This compensation may be accomplished through priorexperimental calibration of the particular flow restriction, e.g. porousdisk, or calculations based on gas flow theory. The modular form enablesthis subsystem to be independently tested and calibrated as well assimplifying assembly and replacement.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. While theforegoing has described what are considered to be the best mode and/orother examples, it is understood that various modifications to theseaspects will be readily apparent to those skilled in the art, and thegeneric principles defined herein may be applied to other aspects. Thus,the claims are not intended to be limited to the aspects shown herein,but is to be accorded the full scope consistent with the languageclaims, wherein reference to an element in the singular is not intendedto mean “one and only one” unless specifically so stated, but rather“one or more.” Unless specifically stated otherwise, the terms “a set”and “some” refer to one or more. Pronouns in the masculine (e.g., his)include the feminine and neuter gender (e.g., her and its) and viceversa. Headings and subheadings, if any, are used for convenience onlyand do not limit the invention.

To the extent that the terms “include,” “have,” or the like are used inthe description or the claims, such terms are intended to be inclusivein a manner similar to the term “comprise” as “comprise” is interpretedwhen employed as a transitional word in a claim.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an illustration of exemplary approaches. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged. Some of the stepsmay be performed simultaneously. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

Terms such as “top,” “bottom,” “front,” “rear” and the like as used inthis disclosure should be understood as referring to an arbitrary frameof reference, rather than to the ordinary gravitational frame ofreference. Thus, a top surface, a bottom surface, a front surface, and arear surface may extend upwardly, downwardly, diagonally, orhorizontally in a gravitational frame of reference.

A phrase such as an “aspect” does not imply that such aspect isessential to the subject technology or that such aspect applies to allconfigurations of the subject technology. A disclosure relating to anaspect may apply to all configurations, or one or more configurations. Aphrase such as an aspect may refer to one or more aspects and viceversa. A phrase such as an “embodiment” does not imply that suchembodiment is essential to the subject technology or that suchembodiment applies to all configurations of the subject technology. Adisclosure relating to an embodiment may apply to all embodiments, orone or more embodiments. A phrase such an embodiment may refer to one ormore embodiments and vice versa.

The word “exemplary” is used herein to mean “serving as an example orillustration.” Any aspect or design described herein as “exemplary” isnot necessarily to be construed as preferred or advantageous over otheraspects or designs.

No claim element is to be construed under the provisions of 35 U.S.C.§112, sixth paragraph, unless the element is expressly recited using thephrase “means for” or, in the case of a method claim, the element isrecited using the phrase “step for.”

What is claimed is:
 1. A flow sensor comprising: a flow restrictiondisposed within a passage such that a fluid passing through the passagemust pass through the flow restriction; an upstream pressure sensorcoupled to the passage at a point upstream of the flow restriction andconfigured to measure and provide an upstream pressure of the fluidwithin the passage; a downstream pressure sensor coupled to the passageat a point downstream of the flow restriction and configured to measureand provide a downstream pressure of the fluid within the passage;pressure sensor electronics coupled to the upstream pressure sensor andthe downstream pressure sensor and configured to determine a pressuredrop measurement; a filter coupled to the passage upstream of theupstream pressure sensor; a temperature sensor coupled to the passageupstream of the filter and configured to measure and provide atemperature of the fluid within the passage; a package for housing theupstream pressure sensor, the downstream pressure sensor, the pressuresensor electronics, and the temperature sensor, wherein the upstreampressure sensor is connected to the passage through a first gas passage,the downstream pressure sensor is connected to the passage through asecond gas passage, and the temperature sensor is connected to thepassage through a feed-through connected to the passage upstream of thefilter; a non-volatile memory configured to store compensationparameters which characterize flow resistance characteristics of theflow restriction, the compensation parameters comprising a pressure dropof at least one predetermined fluid characterized for the flowrestriction; and a flow sensor processor coupled to the memory, theupstream and downstream pressure sensors and the temperature sensor andconfigured to accept measurements therefrom and calculate a compensatedflow rate based at least in part on the measured pressures andtemperature.
 2. The flow sensor of claim 1, wherein: the non-volatilememory is configured to store executable instructions; the flow sensorprocessor is configured by retrieving the executable instructions fromthe memory to further retrieve the compensation parameters from thememory; and the calculation of the compensated flow rate is based atleast in part on the retrieved compensation parameters.
 3. The flowsensor of claim 2, wherein: the flow sensor processor is furtherconfigured to accept an identification of the fluid that is passingthrough the passage; the compensation parameters comprisecharacteristics of the flow restriction that are related to a pluralityof predetermined fluids; the retrieved compensation parameters comprisecharacteristics of the flow restriction related to the identified fluid;and the calculation of the compensated flow rate is based at least inpart on the retrieved compensation parameters that are related to theidentified fluid.
 4. The flow sensor of claim 3, wherein thecharacteristics of the flow restriction are predetermined for each ofthe plurality of predetermined fluids.
 5. The flow sensor of claim 4,wherein the plurality of predetermined fluids comprises one or moremedical gases.
 6. The flow sensor of claim 5, wherein the plurality ofpredetermined fluids comprises one or more of a standard composition ofambient air, a pure oxygen, and a heliox gas mixture.
 7. The flow sensorof claim 4, wherein the characteristics of the flow restriction arepredetermined for each of the plurality of predetermined fluids over arange of temperatures.
 8. The flow sensor of claim 7, wherein the rangeof temperatures comprises at least 5-50° C.
 9. The flow sensor of claim1, wherein the flow restriction comprises a porous disk.
 10. The flowsensor of claim 1, further comprising a temperature sensing elementconnected to the temperature sensor through the feed-through.
 11. Aventilator comprising: a sensor configured to detect a number andplacement of at least one magnet of a gas inlet adapter, the number andplacement of the one or more magnets associated with a gas; an outputflow channel configured to mate with a supply limb; an input flowchannel configured to accept the gas from a source; and a flow sensorcomprising: a flow restriction disposed within a passage coupled betweenthe input flow channel and the output flow channel such that the gaspassing through the passage must pass through the flow restriction; anupstream pressure sensor coupled to the passage at a point upstream ofthe flow restriction and configured to measure and provide an upstreampressure of the gas within the passage; a downstream pressure sensorcoupled to the passage at a point downstream of the flow restriction andconfigured to measure and provide an downstream pressure of the gaswithin the passage; pressure sensor electronics coupled to the upstreampressure sensor and the downstream pressure sensor and configured todetermine a pressure drop measurement; a filter coupled to the passageupstream of the upstream pressure sensor; a temperature sensor coupledto the passage upstream of the filter and configured to measure andprovide a temperature of the gas within the passage; a non-volatilememory configured to store compensation parameters which characterizeflow resistance characteristics of the flow restriction, thecompensation parameters comprising a pressure drop of at least onepredetermined fluid characterized for the flow restriction; a flowsensor processor coupled to the memory, the upstream and downstreampressure sensors and the temperature sensor and configured to acceptmeasurements therefrom and calculate a compensated flow rate based atleast in part on the measured pressures and temperature; and a packagefor housing the upstream pressure sensor, the downstream pressuresensor, and the pressure sensor electronics, the temperature sensor, andthe flow sensor processor, wherein the upstream pressure sensor isconnected to the passage through a first gas passage, the downstreampressure sensor is connected to the passage through a second gaspassage, and the temperature sensor is connected to the passage througha feed-through connected to the passage upstream of the filter.
 12. Theventilator of claim 11, wherein: the non-volatile memory is configuredto store executable instructions; the flow sensor processor isconfigured by retrieving the executable instructions from the memory tofurther retrieve the compensation parameters from the memory; and thecalculation of the compensated flow rate is based at least in part onthe retrieved compensation parameters.
 13. The ventilator of claim 12,further comprising: the gas inlet adapter having the at least one magnetassociated with the gas being supplied to the input flow channel; and acentral processor coupled to the sensor and the flow sensor processor,the central processor configured to identify the gas that will bepassing through the flow sensor from the detected orientation of the gasinlet adapter, wherein: the flow sensor processor is further configuredto accept an identification of the gas that is passing through the flowsensor, the identification based on the number and placement of the atleast one magnet of the gas inlet adapter; the compensation parameterscomprise characteristics of the flow restriction that are related to aplurality of predetermined gases; the retrieved compensation parameterscomprise characteristics of the flow restriction related to theidentified gas; and the calculation of the compensated flow rate isbased at least in part on the retrieved compensation parameters that arerelated to the identified gas.
 14. The ventilator of claim 13, whereinthe characteristics of the flow restriction are predetermined for eachof the plurality of predetermined gases.
 15. The ventilator of claim 14,wherein the plurality of predetermined gases comprises one or moremedical gases.
 16. The ventilator of claim 15, wherein the plurality ofpredetermined gases comprises one or more of a standard composition ofambient air, a pure oxygen, and a heliox gas mixture.
 17. The ventilatorof claim 14, wherein the characteristics of the flow restriction arepredetermined for each of the plurality of predetermined gases over arange of temperatures.
 18. The ventilator of claim 17, wherein the rangeof temperatures comprises at least 5-50° C.
 19. The ventilator of claim11, wherein the flow restriction comprises a porous disk.
 20. Theventilator of claim 11, further comprising a temperature sensing elementconnected to the temperature sensor through the feed-through.